A lens barrel generally includes a plurality of lenses (lens units). In these lens units, an optical axis of the lens may be tilted with respect to an optical axis of the lens barrel due to assembling errors or the like.
Conventionally, when lenses are assembled, in order to adjust such a tilt of a lens (that is, to perform tilt adjustment), a washer having an appropriate width is inserted between a lens frame and a lens holding frame that holds the lens frame (see Patent Document 1).
Moreover, an internal focusing zoom lens that changes a focal position of an optical system by changing the distance between a plurality of lenses to change the magnification of the optical system to move an intermediate lens of the optical system is known (see Patent Document 2).    [Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2006-03837    [Patent Document 2] Japanese Unexamined Patent Application, Publication No. 2000-89086